eta HACK 20, Operation

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Boiler functionality
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clutch so the motor's power is exclusively available for
unblocking the screw. Jammed pieces of wood or even
stones can be easily loosened this way so fuel
transport can resume.
Maximum protection against burn-back
The airtight one-chamber rotary valve keeps the
combustion chamber safely separated from the fuel
deposit in all operating modes. No hot gas can enter
the fuel conveying system and ignition of the wood
chips is impossible. This is the most reliable burn-back
protection possible. Individual pieces of wood that are
too long cannot bring the fuel conveying system to a
halt. They are cut off by a hardened blade on the edge
of the rotary valve chamber.
Optimised ignition
After short breaks in combustion, the refractory-lined
combustion chamber remains hot enough that any
new fuel which is fed in can be ignited by the remaining
embers. The ignition fan only needs to be activated
after long periods without combustion. To save elec-
tricity, the ignition fan is deactivated immediately after
successful ignition, which is recognised by the lambda
probe and exhaust temperature.
Hot combustion chamber with tilting grate
The wood chips are pushed onto the side of the grate
by the stoker screw. A refractory-lined combustion
chamber ensures a clean fire with high burnout tem-
perature. At intervals that depend on the output level,
the grate is tilted by 90° after a controlled ember
burnout in order to automatically remove ash and
foreign bodies from the combustion chamber. Until the
next time the grate is tipped, the ash remains under the
grate and can burn out before it is transported by the
ash screw to the detachable ash box.
Combustion breaks with minimal heat loss
The fire can be regulated between minimum and
maximum output. In autumn and spring, when heating
loads are smaller, the output is regulated by pauses in
combustion. To avoid a build-up of smouldering tar in
the boiler and chimney during these pauses, the fire
undergoes a controlled burnout. Closing the primary
and secondary air flaps ensures that no air can flow
through the boiler in standby, thus preventing unused
heat from being drawn into the flue.
Optimum fuel efficiency with lambda control
Gasification of the wood (output) can be controlled via
the flow of primary air. Through use of the lambda-
controlled secondary air, combustion is kept clean and
highly efficient.
A lack of air means there is not enough oxygen for
complete combustion. On the other hand, too much air
also results in incomplete combustion as it cools the
fire. Below 700°C, not all of the wood gas is burned.
Excessive air also draws too much heat out of the
boiler unused. The lambda probe ensures optimum
combustion and maximum fuel utilisation in everyday
operation.
Turbulent heat exchanger with cleaning
After complete combustion, the hot gas flows into the
cold section of the boiler, where it transfers its heat to
the boiler water. First it flows smoothly through a
downdraft channel for ash sedimentation and then
turbulently through the heat exchanger tubes, which
are equipped with turbulators. The more turbulent the
flow, the more the gas comes into contact with the tube
walls, thus ensuring maximum transfer of heat to the
boiler water. This ensures low exhaust temperatures
and high efficiency.
During cleaning (grate tipping) the turbulators are also
moved to scrape the flue ash from the heat exchanger
tubes. The ash is transported to the ash box by an ash
screw.
Underpressure for maximum safety
A draught fan at the boiler outlet causes underpres-
sure throughout the boiler, thus ensuring high
operational safety without risk of deflagration and
burn-back. The airtight one-chamber rotary valve
makes the usual combustion air fan unnecessary. The
required air is drawn into the combustion chamber
through the regulated primary and secondary air flaps
as a result of the underpressure within the boiler.